This invention relates to novel processes and intermediates for the preparation of pharmaceutically acceptable acid salts, of the formula ##STR1## wherein R.sup.1 H is a pharmaceutically acceptable acid, selected from the group consisting of R.sup.4 SO.sub.3 H, R.sup.4 PO.sub.3 H and YH wherein
R.sup.4 is selected from (C.sub.1 -C.sub.6)alkyl and optionally substituted phenyl or naphthyl wherein the substituent is (C.sub.1 -C.sub.6)alkyl; and PA1 Y is selected from Cl, HSO.sub.4, NO.sub.3, HPO.sub.3 H, and H.sub.2 PO.sub.4, of the naphthyridone antibiotic 7-(1a,5a,6a)-(6-amino-3-azabicyclo3.1.0!hex-3-yl)-1-(2,4-difluorophenyl)- 6-fluoro-1,4-dihydro-4-oxo-1,8-naphthyridine-3-carboxylic acid. PA1 R.sup.4 is selected from (C.sub.1 -C.sub.6)alkyl and optionally substituted phenyl or naphthyl wherein the substituent is (C.sub.1 -C.sub.6)alkyl; and PA1 Y is selected from Cl, HSO.sub.4, NO.sub.3, HPO.sub.3 H, and H.sub.2 PO.sub.4, which comprises treating a compound of the formula ##STR3## wherein R.sup.2 is (C.sub.1 -C.sub.6)alkyl, aryl(C.sub.1 -C.sub.6)alkyl or hydrogen and R.sup.3 is NO.sub.2 or NH.sub.2 ; PA1 a) when R.sup.3 is NH.sub.2 with a compound of the formula R.sup.1 H is as defined above; or PA1 b) when R.sup.3 is NO.sub.2 with a reducing agent in the presence of a compound of the formula R.sup.1 H wherein R.sup.1 H is as defined above. PA1 a) treating a compound of the formula VII with a compound of the formula X--CH.sub.2 --NO.sub.2, wherein X is a leaving group, in the presence of a base to form a compound of the formula VI which is then treated with a reducing agent to form the compound of the formula V; PA1 b) treating the compound of the formula V with a dealkylating agent to form the compound of formula IV; PA1 c) treating the compound of formula IV with a compound of the formula ##STR9## wherein R.sup.2 is as defined above and J is a suitable leaving group, to form a compound of the formula II wherein R.sup.3 is NO.sub.2 ; and PA1 d) treating the compound of formula II, wherein R.sup.3 is NO.sub.2, with a reducing agent comprising hydrogen in the presence of a catalyst or a metal and an acid of the formula R.sup.1 H, as defined above, to form PA1 a) when R is (C.sub.5 -C.sub.10)aryl with hydrogen or .alpha.-chloroethyl chloroformate; or PA1 b) when R is hydrogen, (C.sub.1 -C.sub.6)alkyl with .alpha.-chloroethyl chloroformate.
The antibacterial activity of the aforementioned naphthyridone antibiotic is described in U.S. Pat. Nos. 5,164,402 and 5,229,396 issued Nov. 17, 1992 and Jul. 20, 1993, respectively, the disclosures of which are hereby incorporated herein by reference in their entirety. The foregoing patents are assigned in common with the present application.